1. Field of the Invention
The invention relates generally to unmanned parachutes for cargo drops. More particularly, it relates to a control system and method for targeted landing of cargo using controllable parachutes.
2. Discussion of Related Art
Parachutes have evolved over the years into highly sophisticated systems, and often include features that improve the safety, maneuverability, and overall reliability of the parachutes. Initially, parachutes included a round canopy. A skydiver was connected to the canopy via a harness/container to suspension lines disposed around the periphery of the canopy. Such parachutes severely lacked control. The user was driven about by winds without any mechanism for altering direction. Furthermore, such parachutes had a single descent rate based upon the size of the canopy and the weight of the parachutist.
In the mid-1960's the parasol canopy was invented. Since then, variations of the parasol canopy have replaced round canopies for most applications, particularly for aeronautics and the sport industry. The parasol canopy, also known as gliding or ram air parachute, is formed of two layers of material—a top skin and a bottom skin. The skins may have different shapes but are commonly rectangular or elliptical. The two layers are separated by vertical ribs to form cells. The top and bottom skins are separated at the lower front of the canopy to form inlets. During descent, air enters the cells of the canopy through the inlets. The vertical ribs are shaped to maintain the canopy in the form of an airfoil when filled with air. Suspension lines are attached along at least some of the ribs to maintain the orientation of the canopy relative to the pilot. The canopy of the ram air parachute functions as a wing to provide lift and forward motion. Guidelines operated by the user allow deformation of the canopy to control direction and speed. Ram air parachutes have a high degree of lift and maneuverability.
Despite the increased lift from a ram air parachute, round canopies are still used for cargo drops. However, as tile weight of cargo increases, the size of the canopy must increase to obtain an appropriate descent rate. Reasonable sizes of round parachutes greatly limit the amount of cargo which can be dropped. Therefore, a need exists for a parachute system which can carry additional cargo weight. Additionally, accurate placement of cargo drops from high altitude with round parachutes is impossible. Adjustments can be made for prevailing winds at various altitudes but the cargo is likely to drift off course due to variations. Furthermore, improvements in surface-to-air missiles requires higher altitude drops in order to protect aircraft. In military use, round parachutes are generally used from an altitude around one thousand (1000) feet to ensure accurate placement. However, new, inexpensive, hand held surface-to-air missiles can put in jeopardy airplanes up to twenty-five thousand (25,000) feet in altitude. Current military technique is to use a special forces soldier to pilot both parachute and cargo to the ground from altitudes of twenty-five to thirty-five thousand (25-35,000) feet. This limits cargo to six hundred fifty (650) pounds, as it must be attached to a human. Therefore, a need exists for an autonomous guided parachute system for cargo which can operate at high altitudes as well as scale to heavier cargo weights.
Autonomous ram air parachutes systems have been developed for cargo drops but suffer from several problems that have prevented them from being generally adopted into military techniques. Prior art guided systems include a harness/container system, a single parachute, flight computer, guidance and navigation control software, a GPS, and electric motor actuators. The flight computer must calculate a flight path and glide the system from the drop point all the way to the ground target. In order for the flight computer to accomplish this, the parachute used must b of low wing loading to ensure docile and slow flight. Such lightly loaded parachutes fly with free flight forward speeds of approximately twenty-five (25) miles per hour or slower. Typical wing loadings are around one (1) pound per square foot of wing area. Such slow systems present several problems, first they are greatly effected by winds aloft. At high altitudes winds are quite strong and can be several times the forward speed of the wing. This necessitates the need to map out specific winds at each altitude by dropping radio frequency transmitting sensors units. The collected data must be analyzed and imported to the autonomous systems flight computer to enable a drop position to be calculated and then a flight path. Another problem is the systems time in the air with such light wing loaded parachutes is quite long, increasing their vulnerability and delivery time. Another problem is that higher weight cargo requires proportionally larger wings which become completely impractical far below the maximum weight desired for military use. Therefore, a need exists for an improved autonomous guided parachute system which can provide accurate targeting control from high altitudes, while flying at higher speeds to reduce or negate wind effects, and be able to scale to the ultimate high weight cargo required by militaries.
Typically, static line deployment is used for cargo drops. A line from the harness/container is attached to the cargo hold of the delivery aircraft. The cargo is then pushed out of the hold. The line causes the parachute to be deployed, with or without the use of a drogue. However, air currents around the delivery aircraft can interfere with proper deployment of a gliding parachute using a static line. Also, the cargo is not typically falling stable upon immediate exit which can cause difficulties during opening of the gliding parachute. In order to slightly delay opening, existing systems utilize a double-bag deployment system. However, the double-bag system is complicated and expensive to construct as well as complicated to pack. Therefore, a need exists for an improved system for delaying the deployment of a gliding parachute.
Additionally prior art systems use electric motor actuators and batteries. Typically the motors are overly complicated DC servo drive motors. At high altitudes temperatures are very low. Such systems suffer from the requirement for very large, low power density cold weather batteries. To meet military demand high altitude systems must operate up to −65 F. and existing systems do not function at such temperatures. As such there exists a need for lighter simpler actuators and power system that are unaffected by extreme temperatures.